The present invention relates to directional couplers used in RF applications.
Directional couplers are used in many different RF applications such as power detection and control, test and measurement, mobile phones, and many others.
Numerous types of couplers are known in the art. Micro-strip, strip-line, Lange-couplers and other directional couplers require a large size to obtain a reasonable coupling coefficient and low insertion loss over a wide frequency range. Consequently, this type of coupler increases total size and cost of, for example, mobile devices. L-C couplers used in current power detection applications (GSM, CDMA, WLAN, Bluetooth, etc.) are not “true” directional couplers, and the coupling coefficient depends on a standing wave at the output (load VSWR dependent) resulting in incorrect power measurement and control. On-die implementation of micro-strip and other types of directional couplers is limited by high-frequency applications (microwave and millimeter-wave). The geometry of the coupler is directly proportional to the wavelength of the signal to be detected.
What is desired, therefore, is a true directional coupler for RF applications that can be manufactured with a small geometry and at low cost.